SYMBOLCOMMON_NAMEaka. SYNONYMS
win.lurk (Back to overview)

Lurk


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References
2014-08-07SecureworksBrett Stone-Gross
@online{stonegross:20140807:malware:5bb1963, author = {Brett Stone-Gross}, title = {{Malware Analysis of the Lurk Downloader}}, date = {2014-08-07}, organization = {Secureworks}, url = {https://www.secureworks.com/research/malware-analysis-of-the-lurk-downloader}, language = {English}, urldate = {2019-12-19} } Malware Analysis of the Lurk Downloader
Lurk
Yara Rules
[TLP:WHITE] win_lurk_auto (20221125 | Detects win.lurk.)
rule win_lurk_auto {

    meta:
        author = "Felix Bilstein - yara-signator at cocacoding dot com"
        date = "2022-11-21"
        version = "1"
        description = "Detects win.lurk."
        info = "autogenerated rule brought to you by yara-signator"
        tool = "yara-signator v0.6.0"
        signator_config = "callsandjumps;datarefs;binvalue"
        malpedia_reference = "https://malpedia.caad.fkie.fraunhofer.de/details/win.lurk"
        malpedia_rule_date = "20221118"
        malpedia_hash = "e0702e2e6d1d00da65c8a29a4ebacd0a4c59e1af"
        malpedia_version = "20221125"
        malpedia_license = "CC BY-SA 4.0"
        malpedia_sharing = "TLP:WHITE"

    /* DISCLAIMER
     * The strings used in this rule have been automatically selected from the
     * disassembly of memory dumps and unpacked files, using YARA-Signator.
     * The code and documentation is published here:
     * https://github.com/fxb-cocacoding/yara-signator
     * As Malpedia is used as data source, please note that for a given
     * number of families, only single samples are documented.
     * This likely impacts the degree of generalization these rules will offer.
     * Take the described generation method also into consideration when you
     * apply the rules in your use cases and assign them confidence levels.
     */


    strings:
        $sequence_0 = { ff7508 ff15???????? 8b35???????? 50 ff7508 }
            // n = 5, score = 1100
            //   ff7508               | push                dword ptr [ebp + 8]
            //   ff15????????         |                     
            //   8b35????????         |                     
            //   50                   | push                eax
            //   ff7508               | push                dword ptr [ebp + 8]

        $sequence_1 = { 8b4508 5b 5f 5e c9 c3 55 }
            // n = 7, score = 900
            //   8b4508               | mov                 eax, dword ptr [ebp + 8]
            //   5b                   | pop                 ebx
            //   5f                   | pop                 edi
            //   5e                   | pop                 esi
            //   c9                   | leave               
            //   c3                   | ret                 
            //   55                   | push                ebp

        $sequence_2 = { 56 57 be00001000 56 6a40 ff15???????? 8bf8 }
            // n = 7, score = 800
            //   56                   | push                esi
            //   57                   | push                edi
            //   be00001000           | mov                 esi, 0x100000
            //   56                   | push                esi
            //   6a40                 | push                0x40
            //   ff15????????         |                     
            //   8bf8                 | mov                 edi, eax

        $sequence_3 = { eb20 ff752c ff7528 ff7524 ff7520 }
            // n = 5, score = 800
            //   eb20                 | jmp                 0x22
            //   ff752c               | push                dword ptr [ebp + 0x2c]
            //   ff7528               | push                dword ptr [ebp + 0x28]
            //   ff7524               | push                dword ptr [ebp + 0x24]
            //   ff7520               | push                dword ptr [ebp + 0x20]

        $sequence_4 = { 8b4d08 51 ff15???????? e9???????? 8be5 }
            // n = 5, score = 800
            //   8b4d08               | mov                 ecx, dword ptr [ebp + 8]
            //   51                   | push                ecx
            //   ff15????????         |                     
            //   e9????????           |                     
            //   8be5                 | mov                 esp, ebp

        $sequence_5 = { 53 8bc7 6a0b 99 5b f7fb 8a5415f0 }
            // n = 7, score = 800
            //   53                   | push                ebx
            //   8bc7                 | mov                 eax, edi
            //   6a0b                 | push                0xb
            //   99                   | cdq                 
            //   5b                   | pop                 ebx
            //   f7fb                 | idiv                ebx
            //   8a5415f0             | mov                 dl, byte ptr [ebp + edx - 0x10]

        $sequence_6 = { 59 59 83f801 750d 8d85fcfeffff 50 }
            // n = 6, score = 800
            //   59                   | pop                 ecx
            //   59                   | pop                 ecx
            //   83f801               | cmp                 eax, 1
            //   750d                 | jne                 0xf
            //   8d85fcfeffff         | lea                 eax, [ebp - 0x104]
            //   50                   | push                eax

        $sequence_7 = { ebf8 56 8bf0 33c0 85d2 8bca }
            // n = 6, score = 800
            //   ebf8                 | jmp                 0xfffffffa
            //   56                   | push                esi
            //   8bf0                 | mov                 esi, eax
            //   33c0                 | xor                 eax, eax
            //   85d2                 | test                edx, edx
            //   8bca                 | mov                 ecx, edx

        $sequence_8 = { 85c0 750d 8d85ccfdffff 50 e8???????? 59 8d45cc }
            // n = 7, score = 800
            //   85c0                 | test                eax, eax
            //   750d                 | jne                 0xf
            //   8d85ccfdffff         | lea                 eax, [ebp - 0x234]
            //   50                   | push                eax
            //   e8????????           |                     
            //   59                   | pop                 ecx
            //   8d45cc               | lea                 eax, [ebp - 0x34]

        $sequence_9 = { c1e910 0fb6d1 8b4df4 8b0481 }
            // n = 4, score = 800
            //   c1e910               | shr                 ecx, 0x10
            //   0fb6d1               | movzx               edx, cl
            //   8b4df4               | mov                 ecx, dword ptr [ebp - 0xc]
            //   8b0481               | mov                 eax, dword ptr [ecx + eax*4]

        $sequence_10 = { ff75ec e8???????? 59 83f8ff 7509 c745fc09000000 }
            // n = 6, score = 800
            //   ff75ec               | push                dword ptr [ebp - 0x14]
            //   e8????????           |                     
            //   59                   | pop                 ecx
            //   83f8ff               | cmp                 eax, -1
            //   7509                 | jne                 0xb
            //   c745fc09000000       | mov                 dword ptr [ebp - 4], 9

        $sequence_11 = { 8b4d08 81c190000000 894df4 8b5508 }
            // n = 4, score = 800
            //   8b4d08               | mov                 ecx, dword ptr [ebp + 8]
            //   81c190000000         | add                 ecx, 0x90
            //   894df4               | mov                 dword ptr [ebp - 0xc], ecx
            //   8b5508               | mov                 edx, dword ptr [ebp + 8]

        $sequence_12 = { c1e908 0fb6c1 8b4df4 33948100080000 0fb645ec 8b4df4 039481000c0000 }
            // n = 7, score = 800
            //   c1e908               | shr                 ecx, 8
            //   0fb6c1               | movzx               eax, cl
            //   8b4df4               | mov                 ecx, dword ptr [ebp - 0xc]
            //   33948100080000       | xor                 edx, dword ptr [ecx + eax*4 + 0x800]
            //   0fb645ec             | movzx               eax, byte ptr [ebp - 0x14]
            //   8b4df4               | mov                 ecx, dword ptr [ebp - 0xc]
            //   039481000c0000       | add                 edx, dword ptr [ecx + eax*4 + 0xc00]

        $sequence_13 = { ffd7 85c0 7503 895df8 5f }
            // n = 5, score = 800
            //   ffd7                 | call                edi
            //   85c0                 | test                eax, eax
            //   7503                 | jne                 5
            //   895df8               | mov                 dword ptr [ebp - 8], ebx
            //   5f                   | pop                 edi

        $sequence_14 = { e8???????? 8b450c 8b4d10 8945d4 b824080000 }
            // n = 5, score = 800
            //   e8????????           |                     
            //   8b450c               | mov                 eax, dword ptr [ebp + 0xc]
            //   8b4d10               | mov                 ecx, dword ptr [ebp + 0x10]
            //   8945d4               | mov                 dword ptr [ebp - 0x2c], eax
            //   b824080000           | mov                 eax, 0x824

        $sequence_15 = { 83cefe 46 8a10 8b4d08 }
            // n = 4, score = 800
            //   83cefe               | or                  esi, 0xfffffffe
            //   46                   | inc                 esi
            //   8a10                 | mov                 dl, byte ptr [eax]
            //   8b4d08               | mov                 ecx, dword ptr [ebp + 8]

    condition:
        7 of them and filesize < 5316608
}
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